Historical Context

Bromoil grew out of a theory developed by E.J. Wall and was made workable in 1907 by C. Welborne Piper, building on the oil pigment process that G.E.H. Rawlins had put into practice in 1904. It became a favourite of Pictorialist photographers for its ability to transform ordinary silver gelatin prints into painterly, hand-manipulated images. The process was used by many photographers during the first half of the 20th century before declining with modernism's preference for "straight" photography.

The process exploits the differential swelling of gelatin based on its hardening by silver—shadow areas (more silver, more hardening) accept oil-based ink while highlight areas (less hardening) repel ink when water-swollen.

Chemistry

Bleach-Tanning Bath (Stock)

Component	Amount
Purified water	750 ml
Sulphuric acid, 5%	50 ml
Copper sulphate	60 g
Potassium bromide	60 g
Potassium dichromate	5 g
Purified water to make	1 litre

Dilute 1 part stock with 9 parts water for use.

The dichromate is what tans (hardens) the gelatin in proportion to the silver image. Copper and bromide alone do not tan the gelatin reliably, so a bath without dichromate is not a dependable substitute.

Procedure

Print Preparation

Make print: Print about one grade softer and one stop darker than normal. Fibre-based paper is essential, RC paper does not work, and an unhardened, non-supercoated paper swells best. Kentmere Document Art, long the standard bromoil paper, has been discontinued, so test current papers before committing to an edition.
Fix thoroughly: Double-fix in fresh fixer to ensure complete silver conversion.
Wash: Wash thoroughly (three quarters of an hour to an hour in running water) to remove all fixer.
Dry: Dry completely before bleaching.

Bleaching

Bleach: Immerse the print in the bleach until the image has faded to a faint ghost. Allow at least 6 minutes, or twice the time the image takes to clear if that is longer (AlternativePhotography.com allows up to three times). Do not over-bleach, as this tans the gelatin evenly.
Wash and fix: Wash for 10–15 minutes, until the yellow dichromate stain has cleared (a bath of 2% sodium bisulphite will remove stubborn stain). Fix for about 5 minutes in fresh plain (non-hardening) hypo, then wash for 30 to 45 minutes. Without this fix the image would reappear when the matrix is exposed to light.
Dry: Dry completely. At this stage the print can be stored indefinitely.

Inking

Soak: Soak bleached print in water for 20-30 minutes until gelatin is fully swollen.
Surface preparation: Blot surface water but keep print damp. The gelatin should be swollen but not pooling.
Apply ink: Using a stag's-foot bromoil brush, stipple a stiff lithographic or printing ink onto the print. The hardened shadow areas accept ink; the swollen highlight areas repel it.
Build up: Work gradually, allowing the image to build through successive applications. This is the artistic heart of the process.
Dry: Allow to dry completely.

Inks

Use stiff lithographic inks:

Black: Charbonnel or Graphic Chemical lithographic black
Brown: Burnt sienna, sepia, or custom mixtures
Any colour: Bromoil allows any ink colour or mixture

Thin ink slightly with linseed oil or Burnt Plate Oil if too stiff to work.

Brush Technique

Different brushes produce different effects:

Brush Type	Effect
Stippling	Classic bromoil texture
Sweeping	Directional marks
Dabbing	Varied texture
Multiple brushes	Combine techniques

The hand of the printer is visible in every bromoil—embrace this as a feature, not a flaw.

Troubleshooting

Problem	Likely Cause	Solution
Ink won't adhere	Paper too wet; insufficient hardening	Blot more; longer bleaching
Ink in highlights	Paper too dry; over-inked	More water; lighter touch
Uneven inking	Technique; paper quality	Practice; try different paper
Bleeding edges	Water under edges	Better blotting
Image lost in bleach	Over-bleaching; weak print	Monitor carefully; denser print

Safety

Chemical	Hazard	Precautions
Copper sulphate	Harmful if swallowed; causes skin and serious eye irritation; very toxic to aquatic life	Gloves and eye protection; do not pour down the drain
Potassium bromide	Causes serious eye irritation	Eye protection; gloves
Potassium dichromate	May cause cancer, genetic defects and harm to fertility; fatal if inhaled; toxic if swallowed; corrosive; skin and respiratory sensitiser; oxidiser	Avoid breathing dust: weigh with extraction or a suitable respirator; nitrile gloves and eye protection; dispose of as hazardous waste. Restricted under REACH Annex XIV
Sulphuric acid	Causes severe skin burns and eye damage	Buy ready-diluted; always add acid to water; gloves and eye protection. In the UK, above 15% w/w it is a regulated explosives precursor and the public need a licence
Lithographic ink	Skin irritant; flammable solvents	Gloves; ventilation

Bromoil Transfer

A variation where the inked image is transferred to another surface:

Ink the bromoil as normal
While ink is wet, press face-down onto damp watercolour paper
Run through press or hand-burnish
Peel apart

This produces a reversed image with softer edges and different paper texture.

Sources

An introduction to the bromoil process, National Science and Media Museum
Introduction to Oil and Bromoil printing, AlternativePhotography.com
Potassium dichromate substance information, ECHA
Explosives precursors and poisons: list of chemicals, Home Office (GOV.UK)
The Art of Bromoil and Transfer (David W. Lewis), Photo-Eye Books

This guide combines established practice with community experience. Always follow safety precautions and cross-reference with primary sources before mixing chemicals.

Bromoil

At a glance

Image characteristics

Key chemicals